Systems and methods for ultrasound assisted lipolysis

ABSTRACT

Cells are destroyed within a subcutaneous tissue region using a transducer disposed externally adjacent to a patient&#39;s skin. The transducer emits acoustic energy that is focused at a linear focal zone within the tissue region, the acoustic energy having sufficient intensity to rupture cells within the focal zone while minimizing heating. The transducer may include one or more transducer elements having a partial cylindrical shape, a single planar transducer element coupled to an acoustic lens, or a plurality of linear transducer elements disposed adjacent one another in an arcuate or planar configuration. The transducer may include detectors for sensing cavitation occurring with the focal zone, which is correlated to the extent of cell destruction. A frame may be provided for controlling movement of the transducer along the patient&#39;s skin, e.g., in response to the extent of cell destruction caused by the transducer.

FIELD OF INVENTION

The present invention relates generally to systems and methods fordestroying tissue using focused ultrasound, and more particularly tosystems and methods for destroying tissue by focusing ultrasound from anexternal source towards subcutaneous tissues, such as adipose tissue toaid in body contouring.

BACKGROUND

Liposuction is a commonly used cosmetic surgical procedure for removingfat (adipose) cells to achieve a more desirable body shape. Liposuctionusually involves an invasive surgical procedure, which includespenetrating the skin, melting or shearing the adipose tissue, andmechanically removing the adipose tissue using a vacuum or othersuctioning device.

Tumescent liposuction is a common variation in which “tumescent”solution is introduced into a target tissue region, e.g., a layer offatty tissue, to loosen the structure of the fatty tissue and tofacilitate its suction. The tumescent solution generally includes, amongother possible ingredients, a topical anesthetic, such as lidocaine, anda vasoconstrictor to reduce bleeding, such as Norinephrine. Generally, alarge quantity of tumescent solution is infiltrated, e.g., in aone-to-one ratio with the fat to be removed, causing the tissue regionto swell. Suction is then performed using a special cannula connected toa vacuum system that is introduced into the fatty layer throughincisions in the patient's skin, typically three to six millimeters (3-6mm) wide. The cannula is moved around inside each incision to reachtarget sites within the tissue region that are to be removed.

Traditional liposuction, however, is an extremely invasive, possiblytraumatic procedure. As the cannula is moved through the tissue region,it may damage nerves and/or blood vessels, as well as the fatty tissue.Thus, complications include excessive bleeding, creating a significantrisk of morbidity and/or mortality. Another potential problem withliposuction is lack of uniformity of the patient's final shape due toirregular removal of the fatty tissue.

In recent years, ultrasound has been suggested for assisting inliposuction procedures. For example, ultrasound assisted liposuction(“UAL”) involves introducing a solid stick ultrasound transducer throughan incision in the patient's skin and moving the transducer through afatty tissue region. The transducer emits ultrasonic energy, generallyat frequencies of 20-30 kHz, that may heat the tissue in the regionuntil necrosis occurs, and/or may cause cavitation, thereby rupturingadipose cells in the region. Subsequently, a cannula is introduced intothe tissue region to perform suction, as described above. Alternatively,a hollow transducer may be used that provides suction simultaneouslywith the delivery of ultrasonic energy.

One problem associated with known UAL techniques, however, is that thetransducer may become quite hot during its use. This may result indamage or destruction of tissues adjacent to the target region byoverheating or melting. To protect tissue outside the target region, thetransducer may be introduced through the skin using an insulated sleeve,although this may require a much larger incision, e.g., about tenmillimeters (10 mm) or more wide. In addition, the doctor may need touse extreme care and keep moving the transducer in order to avoidburning tissue. Finally, treatment may also be limited to direct contactbetween the transducer and the adipose tissue, possibly resulting innon-uniform destruction of fat cells in the target region.

As an alternative to UAL techniques, U.S. Pat. No. 5,884,631, issued toSilberg, discloses using an external ultrasonic generator to transmitultrasound waves through a patient's skin to underlying adipose tissue.Silberg proposes using ultrasonic energy at a frequency above abouttwenty kilohertz to disrupt the connective tissue between fat cells,whereupon conventional liposuction may be used to remove the cells. Theultrasound energy in Silberg, however, is not focused, but instead isdelivered from a point contact on the surface of a patient's skinindiscriminately into the underlying tissue. Such unfocused ultrasonicenergy may be ineffective for facilitating liposuction since the energyis merely diffused generally into the underlying tissue.

In addition, noninvasive methods have been proposed for removing adiposetissue. For example, U.S. Pat. No. 5,143,063, issued to Fellner,discloses a device and method for necrosing adipose tissue by directingradiant energy directly to a tissue region or work site. AlthoughFellner generally discloses the use of radiant energy, such as radiofrequency, microwave, or ultrasonic energy, the only specific examplesgiven for focusing ultrasonic energy at a subcutaneous tissue regioninvolve using a concave lens or a Barone reflector. Such a lens orreflector, however, may have a fixed “focal distance,” i.e., thedistance from the device to the “focal zone,” i.e., the region to whichthe energy is focused. In addition, such devices may only generate arelatively small focal zone having a fixed size and shape.

In addition, the exemplary procedure suggested by Fellner involvesfocusing energy at a work site for at least about thirty to fortyminutes in order to effectively heat and necrose tissue at the worksite. Thus, the suggested procedures may be time-consuming and/or mayrisk heating or damaging tissue outside the work site.

Accordingly, systems and methods for destroying subcutaneous tissueand/or for providing more precise monitoring and/or guidance of focusedultrasonic energy used to remove adipose cells or other tissue would beconsidered useful.

SUMMARY OF THE INVENTION

The present invention relates generally to systems and methods forfocusing ultrasound energy from a location external to a patient torupture or otherwise remove cells, such as adipose cells, within asubcutaneous tissue region. The present invention may minimize damage,such as that caused by invasive surgical procedures and/or by heating ofneighboring tissues when unfocused ultrasound is indiscriminatelyintroduced into a tissue region. The target cells, preferably adiposecells, may be ruptured and then removed, for example, by naturalexcretion mechanisms within the body or by gentle suction.

In a preferred method, a transducer is disposed externally adjacent tothe patient's skin. The transducer is driven with drive signals suchthat the transducer emits acoustic energy, while the acoustic energy isfocused at a focal zone within a target tissue region. The acousticenergy, preferably ultrasonic energy, has sufficient intensity tocavitate fluid within the focal zone, thereby rupturing or otherwisedestroying tissue, e.g., adipose cells, within the focal zone. Theultrasonic energy is preferably applied using a relatively low dutycycle, i.e., in short bursts relative to the time between successivebursts to limit the amount of heating of tissue in and around the targettissue region. For example, the transducer may be operated using a dutycycle of about twenty percent (20%) or less, preferably about tenpercent (10%) or less, and more preferably about one percent (1%) orless. Preferably, the transducer may emit ultrasonic energy at afrequency range between about two and ten megahertz (2-10 MHz), and morepreferably between about four and six megahertz (4-6 MHz).

Various embodiments are contemplated for a transducer in accordance withthe present invention. The transducer may have either a fixed focaldistance or a variable focal distance. “Focal distance” is the distancefrom an acoustic emission surface of the transducer to a center of the“focal zone,” i.e., the region where energy from the transducer isfocused. In a preferred embodiment, the transducer is preferablyconfigured for producing a substantially linear focal zone. Thetransducer may have a single transducer element, thereby having a fixedfocal distance. For example, a single partial cylindrical transducer maybe provided that focuses ultrasonic energy due to its geometry, or asubstantially planar transducer may be provided that includes a lens forfocusing the ultrasonic energy at a desired focal zone.

Alternatively, the transducer may include a phased array. For example,the transducer may include a plurality of linear transducer elementsdisposed adjacent to one another, e.g., in a partial cylindricalarrangement or in a substantially planar arrangement. Alternatively, thetransducer may include a plurality of transducer elements definingrespective portions of a single arc, each of which is projected onto aplane. Thus, the plurality of transducer elements may be arranged in aconfiguration similar to a Fresnel lens. Such a transducer configurationmay substantially minimize the space between the acoustic emissionsurface of the transducer and the patient's skin, facilitatingacoustically coupling the transducer to the patient and/or minimizingair gaps between the transducer and the patient's skin.

Drive circuitry is coupled to each individual transducer element, thedrive circuitry being controlled by a controller. Drive signals from thedrive circuitry cause the transducer element(s) to emit ultrasonicenergy. The controller may control a phase shift value of respectivedrive signals to the transducer elements, thereby adjusting a focaldistance to the focal zone.

In yet further embodiments, a transducer array may be provided thatgenerates multiple simultaneous focal zones. These systems may include aplurality of individual transducers that are disposed side-by-side in asubstantially planar configuration, thereby being capable of generatinga plurality of substantially parallel linear focal zones. Treatment timemay be decreased with such a multiple-focal zone embodiment, as will beappreciated by those skilled in the art.

In accordance with another aspect of the present invention, a transducermay be provided that includes one or more detectors for measuringultrasound signals produced during cavitation. Generally, cavitating gasbubbles produce a strong signal, for example, at a frequency ofapproximately one half of the transmitted ultrasound waves. An acousticsensor, such as a cavitation strip detector, may be provided on thetransducer for detecting such cavitation signals.

A monitoring system may be coupled to the detector for monitoringcavitation during a procedure. For example, the system may include aprocessor that correlates the cavitation signals to determine the extentof cavitation, and consequently tissue destruction, occurring in thetarget tissue region. Preferably, a rate of change in amplitude of thedetected signals may be monitored to determine when cells within atarget tissue region have been substantially destroyed. Alternatively,the amplitude of the cavitation signals may be integrated over timeuntil a predetermined value is reached. In addition or alternatively,the system may monitor the cavitation signals to ensure that apredetermined peak amplitude, i.e., rate of cavitation, is not exceeded,e.g., to provide a desired safety factor against excessive cavitation,which may be harmful to the patient.

Additionally, in accordance with another aspect of the presentinvention, an apparatus may be provided for moving an ultrasoundtransducer (or a set of transducers) in a controlled manner. Forexample, the transducer may be mounted to a frame that may be disposedadjacent the patient's skin. The transducer may be moved along thepatient's skin, e.g., continuously or incrementally, to cavitatesuccessively adjacent tissue regions, thereby providing a more uniformtreatment.

Other objects and features of the present invention will become apparentfrom consideration of the following description taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a first preferred embodiment of atransducer and system for treating tissue, in accordance with thepresent invention.

FIG. 2 is a perspective view of the transducer of FIG. 1.

FIG. 3 is a schematic view of a second preferred embodiment of atransducer and system for treating tissue, in accordance with thepresent invention.

FIG. 4 is a cross-sectional view of the transducer and lens of FIG. 3.

FIG. 5 is a schematic view of a third preferred embodiment of atransducer and system for treating tissue, in accordance with thepresent invention.

FIG. 6 is a perspective view of the transducer of FIG. 5.

FIG. 7 is a schematic view of a fourth preferred embodiment of atransducer and system for treating tissue, in accordance with thepresent invention.

FIG. 8 is a perspective view of the transducer of FIG. 7.

FIG. 9 is a cross-sectional view of another preferred embodiment of amultiple-element transducer array, in accordance with the presentinvention.

FIG. 10 is a perspective view of yet another preferred embodiment of amultiple-element transducer array, in accordance with the presentinvention.

FIG. 11 is a cross-sectional view of an alternative embodiment of thetransducer array of FIG. 10.

FIG. 12 is a perspective view of a partial cylindrical transducermovably mounted to a track, in accordance with yet another aspect of thepresent invention.

FIG. 13 is a cross sectional view of a system for treating tissueincluding cavitation detectors, in accordance with another aspect of thepresent invention.

DETAILED DESCRIPTION

Turning to the drawings, FIGS. 1 and 2 show a first preferred embodimentof a system 10 for treating tissue, in accordance with the presentinvention. Generally, the system 10 includes a transducer 12, drivecircuitry 14 coupled to the transducer 12, and a controller 16 coupledto the drive circuitry 14.

The transducer 12 is generally made from piezoelectric material in aconventional manner, as is well known to those skilled in the art. Whenthe transducer 12 is excited by electrical drive signals 15, thetransducer 12 may emit acoustic energy from surface 18, as illustratedby exemplary acoustic waves 20. In the preferred embodiment shown, thetransducer 12 has a single transducer element defining an arcuatecross-section that extends substantially parallel to a longitudinal axis22 of the transducer 12. Thus, the surface 18 defines a portion of acylinder, preferably having a substantially constant radius ofcurvature. Alternatively, the cross-section of the surface 18 may definea portion of another generally concave curve. The term “partialcylindrical” as used herein is intended to include any such variationseven if they define less than half of a cylinder and/or do not have aconstant radius of curvature. In a preferred embodiment, the transducer12 preferably has a base length 24 of between about five and fifteencentimeters (5-15 cm), and a base width 26 of between about one and fourcentimeters (1-4 cm).

Due to the partial cylindrical shape of the transducer 12, the acousticenergy emitted from the surface 18 converges at a focal zone 28.Preferably, the focal zone 28 has a substantially linear shape thatextends substantially parallel to the longitudinal axis 22, as describedfurther below. Because the transducer 12 has only a single transducerelement, a “focal distance” 30, i.e., a distance from the surface 18 toa center of the focal zone 28 along axis “z,” is substantially fixed bythe geometry of the transducer 12. For example, for a constant radiustransducer, the focal distance 30 may correspond substantially to ageometric focus of the transducer 12.

The drive circuitry 14 is coupled to the transducer 12 and providesdrive signals 15 to the transducer 12 that cause the transducer 12 toemit acoustic energy. Preferably, radio frequency (RF) drive signals 15are used to excite the transducer 12 to emit ultrasonic energy at apredetermined amplitude, frequency, and wave shape. In a preferredembodiment, the drive signals 15 cause the transducer 12 to emitultrasonic energy at a frequency between about two and ten Megahertz(2-10 MHz), and more preferably between about four and six Megahertz(4-6 MHz). The optimal frequency may be dependent upon the focaldistance of the focal zone generated by the transducer. For example, ifa longer focal distance is needed, relatively lower frequency drivesignals may be preferred, e.g., to minimize dissipation in theintervening tissue, while for a relatively shorter focal distance,higher frequency drive signals may be preferred.

The controller 16 is coupled to the drive circuitry 14 and controlsvarious aspects of the drive signals 15 provided by the drive circuitry14. For example, the controller 16 may adjust an amplitude of the drivesignals 15, and consequently the amplitude of the acoustic waves 20.Preferably, as described further below, the controller 16 directs thedrive circuitry 14 to cause the transducer 12 to emit acoustic energy atan amplitude or intensity sufficient to cause cavitation, therebydestroying tissue, e.g., rupturing adipose cells, in the focal zone 28.

In a preferred embodiment, the controller 16 activates the drivecircuitry 14 such that the transducer 12 emits acoustic energy using arelatively low “duty cycle,” i.e., a ratio between a time period thatthe transducer 12 is activated during a cycle and a time period of eachcycle. For example, the duty cycle may be about twenty percent (20%) orless, preferably about ten percent or less, and more preferably aboutone percent or less. Thus, the transducer may emit acoustic energy inrelatively short bursts, each burst including only a few discretewavelengths of acoustic energy, but having sufficient intensity to causecavitation and destroy tissue within the focal zone. For example,short-burst pulses may have a duration of between approximately 0.25 and20 μsec may be emitted every 100 μsec during a single sonication.Because the acoustic energy is highly focused and of sufficientamplitude, these short bursts are adequate to rupture or otherwisedestroy cells, e.g., adipose cells, in the focal zone 28. Thus, whilethe acoustic energy radiated during a single burst is relatively high,the time-average acoustic energy emitted by the transducer is relativelylow, thereby minimizing the risk of heat build-up in or adjacent to thetarget tissue region, contrary to previously known hyperthermiatechniques that use heating to necrose tissue.

The transducer 12 is generally disposed in direct contact with apatient's skin 90. Gel or other acoustically conductive media (notshown) may be provided between the transducer 12 and the patient's skin90 to acoustically couple them. Preferably, the acoustic gel fills ahollow space 32 between the transducer 12 and the patient's skin 90 toprevent discontinuities or irregularities in the ultrasonic energyemitted by the transducer 12 that passes through the patient's skin 90.

Alternatively, the transducer 12 may be disposed within a casing, suchas a flexible bag (not shown). An outer surface of the casing may beformed from an acoustically transparent material, such as a thin plasticsheet of mylar or polyvinyl chloride (PVC). More preferably, the outersurface may be substantially flexible to facilitate the casingconforming to the shape of a surface contacted by the casing, such as apatient's skin. The casing may be filled with degassed water, gel, orother acoustically conductive fluid to facilitate acoustically couplingthe transducer to the patient's skin, as is well known in the art.Additional information on such a transducer and casing may be found inU.S. Pat. No. 5,526,814, the disclosure of which is expresslyincorporated herein by reference.

As best seen in FIG. 1, during a lipolysis procedure, the transducer 12is generally placed externally adjacent to the patient's skin 90. Gel orother acoustically conductive material (not shown) is placed between thetransducer 12 and the patient's skin 90, as described above.Alternatively, if the transducer 12 is provided in a casing (not shown),the outer surface of the casing may be placed in contact with thepatient's skin 90, possibly with water, gel, or other acousticallyconductive material placed between the casing and the patient's skin 90to provide additional acoustical coupling, if desired. The acousticallyconductive material may act as a spacer to allow focusing of theacoustic energy at different depths within the tissue, as describedfurther below.

The patient's skin 90 includes a layer of epidermis overlying a layer ofdermis 92, which, in turn, generally overlies a subcutaneous tissuelayer including fatty (adipose) tissue 94. The transducer 12 ispositioned a predetermined distance above the patient's skin 90 suchthat the focal zone 28 of the transducer 12 is positioned within thesubcutaneous tissue region 94. For example, if the transducer 12 ismounted in a casing, the casing may be sufficiently flexible toaccommodate a range of positions above the patient's skin 90 withoutdecoupling the casing from the patient's skin 90.

The transducer 12 is then activated, causing acoustic energy topenetrate through the epidermis and dermis 92 into the fatty tissuelayer 94, and converge substantially at the focal zone 28. Preferably,during a “sonication,” i.e., a single treatment during which acousticenergy is focused at a target tissue region for a set time period, thetransducer 12 may be activated for a plurality of successive relativelyshort bursts, as described above, to substantially destroy the tissue inthe focal zone 28.

“Cavitation” is a well-known phenomenon experienced when acoustic energyencounters matter. Generally, the acoustic energy causes gas bubblesdissolved in fluid within the tissue to “pop,” thereby releasing kineticenergy. For example, the acoustic energy may be absorbed by water intissue, causing gas bubbles dissolved in the water to rapidly contractand expand, and consequently explode or “pop.” Alternatively, otherexisting gas bubbles occurring within the tissue may be cavitated usingacoustic energy. The released kinetic energy may rupture cells or loosenconnective tissue adjacent to the cavitated gas bubbles.

In a further alternative, gas bubbles, e.g., dissolved in a liquid, maybe introduced into the target tissue region before the transducer 12 isactivated. For example, a “tumescent” solution may be injected into thetarget tissue region that includes gas bubbles, such as air or Nitrogen,dissolved therein. The tumescent solution may also include a variety ofknown materials that may enhance a lipolysis procedure. For example, thetumescent solution may include a topical anesthetic, such as lidocaine,or a vasoconstrictor, such as Norinephrine. Thus, in addition toproviding gas bubbles to promote cavitation, the tumescent solution mayhelp reduce pain to the patient, may reduce bleeding, may cause tissuewithin the target tissue region to swell, may help loosen fatty tissue,and the like, as is well known in the art.

The tumescent solution may be injected into the target tissue regionbefore the transducer is positioned adjacent the patient's skin. If theultrasound treatment is to be followed by gentle suction, largequantities of tumescent solution may be infiltrated into the tissue, forexample, in a one-to-one or less ratio with the fat tissue to beremoved, e.g., to loosen the tissue. The kinetic energy released by thecavitating gas bubbles preferably causes the walls of cells in the focalzone, such as adipose cells, to rupture, releasing cell media into theinterstitial space between the cells, e.g., causing the subcutaneousadipose tissue 145 to become emulsified. The transducer 12 may then bemoved to another location, for example, adjacent to the first targettissue region, and the procedure repeated.

Alternatively, other gas bubble-containing fluids may be introduced. Forexample, ultrasound contrast agents, such as liquids includingmicrospheres containing lipids or other materials, may be injected intothe tissue region. In a further alternative, free gas bubbles suspendedin a liquid may be injected.

Preferably, the transducer 12 is successively moved incrementally orcontinuously in a direction substantially perpendicular to itslongitudinal axis 18 and activated, thereby causing cavitation through alayer of subcutaneous tissue. To assist in this method, the transducer12 may be movably mounted to a frame 650, such as that shown in FIG. 12,and described further below. This may allow the target cells to beruptured in a substantially uniform manner until a generally planarlayer of subcutaneous tissue, e.g., a layer of adipose tissue, iscavitated.

Turning to FIGS. 3 and 4, an alternative embodiment of a system 110 inaccordance with the present invention is shown that includes atransducer 112 having a single, substantially planar transducer element134 and an acoustic lens 136. The system 110 also includes drivecircuitry 14 and a controller 16, similar to the embodiment describedabove. The lens 136 is acoustically coupled to the transducer element134, thereby focusing ultrasonic energy, represented by exemplary waves120, emitted by the transducer element 134 at a focal zone 128. The lens136 may be substantially permanently or detachably attached to thetransducer element 134. Alternatively, the lens 136 may be spaced apredetermined distance from the transducer element 134, and anacoustically conductive material may be disposed between the transducerelement 134 and the lens 136.

Preferably, the lens 136 defines a partial cylindrical emission surface118, more preferably having an elongate concave shape, for focusing theacoustic energy generated by the transducer element 134 at asubstantially linear focal zone 128 that extends substantially parallelto a longitudinal axis 122 of the transducer 112. In the preferredembodiment shown, the lens 136 has an elongate concave emission surface118, although alternatively an elongate convex emission surface (notshown) may be provided depending upon the material of the lens 136.Because a focal distance 130 to the focal zone 128 is substantiallyfixed by the geometry of the lens 136, the transducer 134 may be movedcloser or farther away from the patient's skin 90 to change the locationof the focal zone 128 within the subcutaneous tissue region 94. In analternative embodiment, the lens 136 may be replaced with another lens(not shown) having a different radius of curvature, to provide a desiredfocal distance 130 to the focal zone 128. In a further alternative, anacoustic lens may be provided that allows adjustment of the focaldistance, such as that disclosed in co-pending application Ser. No.09/557,185, filed Apr. 21, 2000, the disclosure of which is expresslyincorporated herein by reference.

Referring now to FIGS. 5 and 6, another preferred embodiment of a system210 in accordance with the present invention is shown that includes atransducer 212, drive circuitry 214, and a controller 216. Thetransducer 212 includes a plurality of transducer elements (234-1 to234-n), each transducer element 234 preferably extending substantiallyparallel to a longitudinal axis 222. More preferably, the transducerelements 234 are arranged in a linear configuration, i.e., side-by-sidein a lengthwise manner, thereby together defining a partial cylindricalemission surface 218. In an alternative embodiment, shown in FIGS. 7 and8, a transducer 312 may include a plurality of transducer elements 334disposed in a substantially planar configuration extending substantiallyparallel to longitudinal axis 322.

The transducer 212 may be formed from a plurality of individualtransducer elements 234 that are bonded together. Alternatively, thetransducer 212 may be formed from a single piece of piezoelectricmaterial, with grooves formed therein to separate and define eachtransducer element 234. Any spaces (not shown) between the transducerelements 234 may be filled with silicone and the like to substantiallyisolate the transducer elements 234 from one another, as is well knownto those skilled in the art. The transducer 212 may include betweenabout three and thirty, and preferably between three and ten, transducerelements 234.

The drive circuitry 214 is individually coupled to each transducerelement 234 to deliver respective drive signals 215 to the transducerelements 234. The controller 216 is coupled to the drive circuitry 214for controlling several aspects of the drive signals 215 generated bythe drive circuitry 214. First, the controller 216 may control theamplitude of the drive signals 215, for example, to control theintensity of ultrasonic energy delivered by the transducer 212, similarto the embodiments described above. In addition, the controller 216 maycontrol a phase shift value between each of the transducer elements 234.For example, by shifting the phase between the transducer elements 234-1to 234-n, the focal distance 230 to the focal zone 228 may be adjustedalong the z-axis. The controller 216 may include a processor, such as amicrocomputer (not shown), that is coupled to the drive circuitry 214for controlling these aspects of its operation.

Referring now to FIG. 9, another embodiment of a system 410, inaccordance with the present invention, is shown that includes atransducer 412, drive circuitry 414, and a controller 416. Thetransducer 512 includes a plurality of transducer elements 434-1 to434-n formed from piezoelectric material, similar to the embodimentsdescribed above. The transducer elements 434 have a cross-sectioncorresponding substantially to respective portions of a cylinder 438(shown in phantom) that are projected generally onto a plane (defined bythe surface of the patient's skin 90 in FIG. 9). Thus, the transducer412 may include an emission surface 418 that corresponds substantiallyto a partial cylinder 438, but may substantially minimize a cavity 432between the transducer 412 and the patient's skin 90. This configurationhas a geometry somewhat similar to an optical lens, called a Fresnellens, which is a transparent panel used to focus light passing throughit.

The drive circuitry 414 is coupled to the individual transducer elements434 for supplying drive signals 415, similar to the embodimentsdescribed above. The transducer 412 emits acoustic energy similar to thepartial cylinder 438, with the discontinuity between adjacent transducerelements being substantially negligible. The distance that thetransducer elements 434 are projected from the partial cylinder 438 mayrequire compensation to ensure proper focusing. Preferably, thecontroller 416 controls the drive circuitry 414 to introduce phaseshifts into the drive signals 415 to compensate for the distance betweenthe transducer elements 434 and the portion of the partial cylinder 438from which the respective transducer elements 434 are projected. Thus,the inner transducer elements 434-2 to 434-(n−1) may emit acousticenergy having predetermined delays relative to the outer transducerelements 434-1 and 434-n such that the acoustic energy delivered tofocal zone 428 has similar properties to acoustic energy that would beemitted by the partial cylinder 438.

The transducer 412 may be placed in contact with a patient's skin 90,with acoustic gel or similar material provided within the cavity 432 toacoustically couple the transducer 412 to the patient. Because of thesubstantially planar configuration of the transducer 412, significantlyless acoustic gel may be required, thereby reducing the possibility ofdiscontinuities between the transducer 412 and the patient's skin 90.Acoustic energy may then be delivered through the epidermis and dermis92 into a subcutaneous fatty tissue layer 94 and focused at focal zone428. The controller 416 may introduce phase shifting to compensate forthe transducer configuration, as well as providing further phaseshifting to control a focal distance 430 and/or size and shape of thefocal zone 428, similar to the embodiments described above.

In an alternative embodiment, a multiple element transducer device maybe provided that is coupled to an acoustic lens having a configurationsimilar to a Fresnel lens. For example, a transducer device (not shown)may be provided that includes a substantially planar transducer array,such as that shown in FIGS. 7 and 8. A lens, configured similar to thetransducer 412, may be coupled to the emission surface of such atransducer array to provide further focusing of acoustic energy emittedby the transducer array.

Referring now to FIG. 10, an alternative embodiment of a transducerarray 512 is shown that includes a plurality of transducers 534-1 to534-p arranged side-by-side in a substantially planar configurationdisposed substantially parallel to longitudinal axis 522. Each of thetransducers 534 may be similar in construction to any of the transducersdescribed above. The transducers 534 may be connected to one anotherand/or may be provided on a track, such as the frame described below.

During use, the transducer array 512 may be acoustically coupled to apatient (not shown), for example, by placing the transducers 534 incontact with or in close proximity to the patient's skin (also notshown). Any spaces between the transducers 534 and the skin may befilled with an appropriate acoustically conductive medium, such as anacoustic gel (not shown) that may have a density similar to the tissuebeing treated, e.g., adipose tissue. The transducers 534 may beactivated to generate a plurality of substantially parallel focal zones528-1 to 528-p. The transducer array 512 may be moved along the surfaceof the patient's skin, e.g., along a Y-axis, i.e., substantiallyperpendicular to the longitudinal axis 522 and z-axis, thereby rupturingor otherwise destroying a layer of tissue, e.g., a layer of adiposetissue (also not shown).

Thus, the transducer array 512 may only have to be moved a distanceequal to a distance between adjacent transducers 534 in order to removea layer of tissue beneath the transducer array 512. This may provide asignificantly shorter treatment time than using a single transducer, aswill be appreciated by those skilled in the art. Alternatively, as shownin FIG. 11, transducer array 512′ may include a plurality of transducers534-1′ to 534-n′ that have progressively deeper focal distances 530-1′to 530′n′. Thus, as the transducer array 512 is moved along a patient'sskin 90, several layers of tissue within tissue region 94 may besubstantially simultaneously cavitated.

In a further alternative, the transducer array may be provided within afluid-filled casing (not shown), such as that described above, that maybe placed in contact with a patient's skin. The transducer array may bemoved within the casing, e.g. incrementally or continuously,substantially parallel to the surface of the patient's skin. Thus, asingle layer or multiple layers of tissue may be removed without havingto directly contact the patient's skin with the transducer or move thetransducer directly along the patient's skin.

Turning to FIG. 12, the various embodiments of transducers describedherein, designated generally as 612, may be movably mounted to a frame650. The frame 650 may include a pair of spaced apart rails 652extending along a Y-axis of the frame 650. The transducer 612 may beslidably mounted to the rails 652,for example, in tracks (not shown).Alternatively, the frame 650 may be mounted within a casing (not shown)as described above. Preferably, the frame 650 is substantially flat oris contoured similar to a corresponding region of a patient's body (alsonot shown). Thus, the transducer 612 may be moved along the rails whileremaining substantially constantly in contact with the patient's body.

In one embodiment, the frame 650 may facilitate manual manipulation ofthe transducer 612 with respect to the patient's body. The transducer612 may be coupled to the patient's skin (not shown), e.g., by providingacoustic gel and the like in the cavity 632 and/or elsewhere between thetransducer 612 and the patient's skin. The transducer 612 may be movedalong the frame 650 to a desired location, and then activated tocavitate an underlying tissue region.

Preferably, the frame 650 may facilitate motorized and/or automaticoperation of the transducer 612. As shown in FIG. 13, a mechanicalcontroller 664, e.g., including a motor (not shown), may be coupled tothe frame 650, e.g., to the track (not shown) in the rails 652, ordirectly to the transducer 612. The controller 664 may allow thetransducer 612 to be moved incrementally, continuously, and/or basedupon desired feedback along the Y-axis, i.e., in a directionsubstantially perpendicular to a longitudinal axis 622 of the transducer612. For example, the transducer 612 may be automatically moved to adesired location, activated for a predetermined time, moved to anadjacent location, activated again, and so on to destroy or remove alayer of tissue, e.g., to provide a more uniform lipolysis of a layer ofadipose tissue.

In accordance with another aspect of the present invention, one or morecavitation detectors may be associated with any of the transducersdescribed herein. The cavitation detectors may facilitate controlling atreatment, e.g., to more evenly and uniformly destroy a layer of tissue,or may be provided as a safety feature. Turning to FIG. 13, in apreferred embodiment, cavitation strip detectors 660 may be provided onopposing edges of a transducer 612. The detectors 660 may be betweenabout one and two millimeters (1-2 mm) wide, and may extendsubstantially the entire length of the transducer 612. The detectors 660may be coupled to a monitoring system 662, e.g., for monitoringcavitation within the focal zone 628 of the transducer 612.

In one embodiment, the monitoring system 662 includes a meter (notshown), which may provide an output, e.g., on a gauge or other display,based upon signals detected by the detectors 660. As gas bubbles in thefocal zone are cavitated, they produce ultrasonic signals, and inparticular, may produce relatively strong signals at approximately halfof the frequency of the original or incident ultrasound waves. Thedetectors 660 may be configured for detecting such cavitation signalsproduced at the focal zone 628 of the transducer 612. Thus, a physicianperforming a lipolysis procedure may monitor the cavitation signalsusing the detectors 660 to ensure that a desired level of cavitation isoccurring and/or that a predetermined maximum level of cavitation is notexceeded.

Alternatively, the monitoring system 662 may be coupled to a controller616 and/or drive circuitry 614 that are used to drive the transducer612. For example, the monitoring system 662 may notify the controller616 when a maximum level of cavitation is exceeded (which may be presetby the user), whereupon the controller 616 may direct the drivecircuitry 614 to automatically discontinue drive signals 615 to thetransducer 612. The controller 616 may then require resetting by thephysician before the transducer 612 may be used for any furthertreatment, or the controller 616 may only discontinue the drive signals615 for a predetermined time, e.g., to provide sufficient time for thetissue to recover. Thus, the detectors 660 may provide a desired safetyfactor during a treatment.

In a further alternative, the controller 616 may adjust an amplitude ofthe drive signals 615 in response to the cavitation signals detected bythe detectors 660. The controller 616 may correlate the amplitude of thecavitation signals to an extent of cell destruction occurring at thefocal zone 628. More preferably, the controller 616 may correlate a rateof change of amplitude of the cavitation signals over time to determinethe extent that cells have been ruptured within the focal zone. Thus, ifcavitation is occurring at too great a rate, which may excessivelydamage tissue in or adjacent to the focal zone, the amplitude of thedrive signals 615 may be reduced accordingly.

In addition or alternatively, the monitoring system 662 may be coupledto a mechanical controller 664 for moving the transducer 612 within aframe 650. For example, the intensity of the cavitation signals, andpreferably a rate of change in intensity of the cavitation signals maybe correlated to an empirical database to automatically determine when adesired level of cell destruction has occurred within the focal zone628. When a predetermined rate of change is detected, e.g., the rate ofchange begins to drop at a predetermined rate, the mechanical controller664 may automatically move the transducer 612 to a new and/or adjacentlocation. Alternatively, the amplitude of the cavitation signals may beintegrated over time until a predetermined value is reached, indicatingthat a desired level of cell destruction has occurred. The drive signals615 to the transducer 612 may be discontinued until the transducer 612is moved to the new location.

Thus, for example, cavitation strip detectors 660 may facilitatemonitoring whether lipolysis is proceeding smoothly and substantiallyuniformly. As the transducer 612 is moved across a patient's skin (notshown) with the intention to destroy a substantially uniform layer ofadipose tissue, it may be used to determine when the transducer shouldbe moved to the next position. Preferably, the monitoring system 662 maybe coupled to the cavitation strip detectors 660 for correlatingcavitation signals detected by the cavitation detectors to facilitatemonitoring and/or ensuring a more even rupturing of cells within a layerof fatty tissue. Such a monitoring system 662 may facilitate moreuniform cell destruction and may help deliver adequate energy to a givenfocal zone, thereby preventing overheating or corollary damage toneighboring tissues. Thus, the cavitation strip detectors 660 mayprovide real-time control and feedback for producing a more uniformremoval of the adipose layer.

Although the exemplary methods described herein include lypolysis, i.e.,destroying or removing adipose tissue, it will be appreciated that thesystems and methods of the present invention may be used for treating avariety of subcutaneous tissues. For example, the systems and methods ofthe present invention may be used to destroy tumors within subcutaneoustissue, such as cancerous tumors, without invasive surgery. Chemotherapyagents may be introduced into a target tissue region before the systemsare used to cause cavitation within the tissue region. The ultrasoniccavitation pulse may cause the membranes of cells within the tissueregion to become porous, even if the cells are not totally destroyed.This may enhance the effectiveness of the chemotherapy agents on thecells within the tissue region, as will be appreciated by those skilledin the art.

While the invention is susceptible to various modifications, andalternative forms, specific examples thereof have been shown in thedrawings and are herein described in detail. It should be understood,however, that the invention is not to be limited to the particular formsor methods disclosed, but to the contrary, the invention is to cover allmodifications, equivalents and alternatives falling within the scope ofthe appended claims.

What is claimed is:
 1. A system for destroying tissue within asubcutaneous tissue region, comprising: a transducer device comprisingan emission surface for emitting acoustic energy and defining alongitudinal axis, the transducer device configured for focusing theacoustic energy at a substantially linear focal zone that extendssubstantially parallel to the longitudinal axis in the subcutaneoustissue region; drive circuitry coupled to the transducer device forproviding drive signals to the transducer device whereby the transducerdevice may emit acoustic energy from the emission surface; and acontroller coupled to the drive circuitry, the controller configured forcontrolling the drive signals delivered by the drive circuitry such thatthe acoustic energy emitted by the transducer device has sufficientintensity to cause cavitation and destroy cells within the focal zone,the controller configured for controlling the drive circuitry such thatthe transducer has a duty cycle of about twenty percent (20%) or less tominimize heating within the focal zone.
 2. The system of claim 1,wherein the drive circuitry is configured for providing drive signalshaving a frequency ranging from approximately 0.25 MHz to 30 MHz.
 3. Thesystem of claim 1, wherein the transducer device has a partialcylindrical emission surface extending substantially parallel to alongitudinal axis of the transducer.
 4. The system of claim 3, whereinthe transducer device comprises a substantially planar transducerelement and a partial cylindrical lens defining the emission surface,the lens acoustically coupled to the planar transducer element forfocusing the acoustic energy at the substantially linear focal zone. 5.The system of claim 3, wherein the emission surface is concave and has apredetermined radius of curvature for focusing the acoustic energy at apredetermined focal distance from the emission surface to the focalzone.
 6. The system of claim 3, wherein the transducer device comprisesone or more transducer elements disposed in an elongate arcuateconfiguration, the emission surface comprising an elongate concave innersurface of the one or more transducer elements.
 7. The system of claim6, wherein: the transducer comprises a plurality of linear transducerelements disposed adjacent one another and extending substantiallyparallel to the longitudinal axis of the transducer; the drive circuitryis configured for providing respective drive signals to each of thelinear transducer elements; and the controller is configured forcontrolling a phase of the respective drive signals to adjust a focaldistance from the emission surface to the focal zone.
 8. The system ofclaim 1, wherein the transducer comprises a plurality of elongate lineartransducer elements disposed adjacent one another in a substantiallyplanar configuration.
 9. The system of claim 8, wherein the drivecircuitry is configured for providing respective drive signals to eachof the linear transducer elements, and wherein the controller isconfigured for controlling a phase of the respective drive signals toadjust a focal distance from the emission surface to the focal zone. 10.The system of claim 1, wherein the transducer device comprises aplurality of transducers disposed adjacent to one another, thetransducers configured for generating respective substantially linearfocal zones that extend generally parallel to one another.
 11. Thesystem of claim 10, wherein a first of the plurality of transducers hasa first focal distance and wherein a second of the plurality oftransducers has a second focal distance that is different than the firstfocal distance.
 12. The system of claim 1, further comprising a frame towhich the transducer device is mounted, the transducer device beingmovable along the frame for moving the focal zone to successive tissueregions.
 13. The system of claim 1, wherein the controller is configuredfor controlling the drive circuitry such that the transducer has a dutycycle of about ten percent (10%) or less.
 14. The system of claim 1,wherein the controller is configured for controlling the drive circuitrysuch that the transducer has a duty cycle of about one percent (1%) orless.
 15. The system of claim 1, wherein the transducer device comprisesa plurality of transducer elements defining respective portions of anarc projected generally onto a plane.
 16. A method for destroying cellswithin a subcutaneous tissue region located beneath a patient's skin,comprising: disposing a transducer defining a longitudinal axisexternally adjacent to the patient's skin; and driving the transducerwith drive signals using a relatively low duty cycle such that thetransducer emits acoustic energy, while focusing the acoustic energyfrom the transducer at a substantially linear focal zone extendingsubstantially parallel to the longitudinal axis within the tissueregion, the acoustic energy having sufficient intensity to cavitatecells within the focal zone while substantially minimizing heating oftissue within the focal zone.
 17. The method of claim 16, wherein theacoustic energy has a frequency ranging from approximately 0.25 MHz to30 MHz.
 18. The method of claim 16, wherein the transducer comprises anacoustic emission surface defining a portion of a cylinder for focusingthe acoustic energy at the substantially linear focal zone.
 19. Themethod of claim 18, wherein the transducer comprises a plurality oftransducer elements disposed substantially parallel to the longitudinalaxis, and wherein the step of driving the transducer comprisescontrolling a phase of the drive signals to adjust a focal distance tothe focal zone.
 20. The method of claim 18, wherein the transducercomprises a generally planar transducer and an acoustic lens definingthe emission surface, and wherein the acoustic energy is focused at thefocal zone by directing the acoustic energy through the acoustic lens.21. The method of claim 18, wherein the transducer comprises an arcuatetransducer extending substantially parallel to the longitudinal axis.22. The method of claim 16, further comprising moving the transducer ina direction substantially perpendicular to the longitudinal axis of thetransducer, thereby moving the focal zone to a position substantiallyparallel to a previous position within the tissue region.
 23. The methodof claim 22, wherein the transducer is mounted to a frame, thetransducer being movable along the frame in a direction substantiallyperpendicular to the longitudinal axis of the transducer.
 24. The methodof claim 16, further comprising introducing a fluid into the tissueregion, the fluid comprising gas bubbles for enhancing cavitation withinthe tissue region.
 25. The method of claim 16, wherein the subcutaneoustissue region comprises adipose tissue, and wherein the ruptured cellscomprise adipose cells.
 26. A system for treating tissue within asubcutaneous tissue region, comprising: a transducer device comprising aplurality of transducer elements defining respective portions of an arcprojected generally onto a plane, thereby providing an emission surfaceextending substantially parallel to a longitudinal axis of thetransducer device, the emission surface configured for emitting acousticenergy at a substantially linear focal zone extending substantiallyparallel to the longitudinal axis; drive circuitry coupled to thetransducer device for providing drive signals to the transducer devicewhereby the transducer device may emit acoustic energy from the emissionsurface; and a controller coupled to the drive circuitry, the controllerconfigured for controlling the drive signals delivered by the drivecircuitry to focus the acoustic energy at the substantially linear focalzone.
 27. The system of claim 26, wherein the drive circuitry isconfigured for providing respective drive signals to each of the lineartransducer elements, and wherein the controller is configured forcontrolling a phase of the respective drive signals to adjust a focaldistance to the focal zone.
 28. The system of claim 26, wherein thecontroller is configured for activating the drive circuitry inrelatively short-burst pulses to provide a relatively low duty cycle ofthe transducer.
 29. The system of claim 28, wherein the duty cycle isabout twenty percent or less.
 30. The system of claim 26, furthercomprising a frame to which the transducer device is mounted, thetransducer device being movable along the frame for moving the focalzone to successive tissue regions.
 31. A system for destroying cellswithin a subcutaneous tissue region, comprising: a transducer devicecomprising an emission surface for emitting acoustic energy, thetransducer device configured for focusing the acoustic energy at asubstantially linear focal zone within the subcutaneous tissue region;drive circuitry coupled to the transducer device for providing drivesignals to the transducer device whereby the transducer device emitsacoustic energy from the emission surface; a controller coupled to thedrive circuitry, the controller configured for controlling the drivesignals delivered by the drive circuitry such that the acoustic energyemitted by the transducer device has sufficient intensity to causecavitation and destroy cells within the focal zone; a cavitationdetector mounted in a predetermined arrangement with the transducerdevice such that the cavitation detector is oriented towards the focalzone, the detector configured for sensing cavitation within the focalzone; and a monitoring system coupled to the cavitation detector, themonitoring system configured for correlating cavitation signalsgenerated by the cavitation detector to determine an extent of celldestruction occurring within the focal zone.
 32. The system of claim 31,wherein the monitoring system is configured for correlating a rate ofchange in intensity of the cavitation signals with the extent of celldestruction occurring within the focal zone.
 33. The system of claim 31,wherein the monitoring system is configured for integrating thecavitation signals over time until a predetermined value is reached. 34.The system of claim 31, further comprising a frame to which thetransducer is mounted, the transducer being movable along the frame formoving the focal zone to successive tissue regions.
 35. The system ofclaim 34, further comprising a mechanical controller for moving thetransducer along the frame.
 36. The system of claim 35, wherein themechanical controller is coupled to the monitoring system and configuredfor automatically moving the transducer to a new location along theframe when a predetermined extent of cell destruction is determined bythe monitoring system.
 37. The system of claim 31, wherein thetransducer device comprises a plurality of transducers disposed in asubstantially planar arrangement, the transducers being configured forgenerating substantially linear focal zones that extend substantiallyparallel to one another.
 38. The system of claim 37, wherein thetransducer device comprises a first transducer configured for focusingacoustic energy at a first focal distance a second transducer configuredfor focusing acoustic energy at a second focal distance different fromthe first focal distance.
 39. A method for destroying cells within asubcutaneous tissue region using a transducer mounted to a frame, themethod comprising: disposing the frame in close proximity to an externalsurface of a patient with the transducer oriented towards thesubcutaneous tissue region; driving the transducer with drive signalssuch that the transducer emits acoustic energy while focusing theacoustic energy from the transducer at a substantially linear focal zonewithin the tissue region, thereby causing cavitation and destroyingcells within the focal zone; monitoring cavitation within the focalzone; correlating the cavitation within the focal zone with an extent ofcell destruction within the focal zone; and automatically moving thetransducer along the frame to a new location along the external surfaceof the patient when a predetermined level of cell destruction within thefocal zone is obtained.
 40. The method of claim 39, wherein thecavitation is monitored by one or more cavitation detectors.
 41. Themethod of claim 40, wherein the cavitation detectors comprise acousticsensors that produce signals in response to cavitation within the focalzone, and wherein the signals are compared to a database to correlatethe cavitation occurring within the focal zone to the extent of celldestruction.
 42. The method of claim 41, wherein a rate of change inamplitude of the signals is correlated with an empirical database todetermine when the predetermined level of cell destruction is obtained.43. The method of claim 42, wherein the cavitation detectors compriseacoustic sensors that produce signals in response to cavitation withinthe focal zone, and wherein the signals are integrated over time until apredetermined value is reached, the predetermined value corresponding tothe predetermined level of cell destruction.
 44. The method of claim 39,wherein the transducer simultaneously generates multiple substantiallylinear focal zones when driven by the drive signals.
 45. The method ofclaim 44, wherein the multiple substantially linear focal zones arefocused at different focal distances, such that multiple layers oftissue are substantially simultaneously destroyed by the transducer. 46.The method of claim 39, wherein the transducer is moved incrementallyalong the frame when a predetermined level of cell destruction isobtained within successive focal zones.
 47. The method of claim 39,further comprising introducing a fluid into the tissue region, the fluidcomprising gas bubbles for enhancing cavitation within the tissueregion.
 48. The method of claim 39, wherein the subcutaneous tissueregion comprises adipose tissue, and wherein the ruptured cells compriseadipose cells.